1. Field of the Invention
This invention relates to a liquid crystal display device to be used for displays such as in portable TV sets and lap-top personal computers, for example.
2. Description of the Related Art
The liquid crystal displays (liquid crystal display devices) weigh light, permit a decrease in thickness, and consume only a small amount of electric power and, owing to these benefits, have found utility in such applications as displays for portable TV sets and lap-top personal computers. Research directed to the development of liquid crystal displays of larger dimensions and higher degrees of accuracy are now underway.
As a matrix substrate for driving a liquid crystal, the active matrix substrate which has mutually intersecting sets each of a plurality of address wires and data wires and a thin-film transistor (or MIM element) formed of amorphous Si (hereinafter referred to briefly as "a-Si") or poly Si (hereinafter referred to briefly as "p-Si"), for example, laid out on a substrate has been known. The liquid crystal display device is constructed by airtightly interposing a liquid crystal between this liquid crystal-driving active matrix substrate and a counter substrate.
Incidentally, the liquid crystal-driving active matrix substrate of this sort is generally tested, during the process of production, to conform the effective lighting condition of the component picture elements and detect any possible line defect in address wires and data wires, for example.
As a means for protecting the liquid crystal-driving active matrix substrate of this sort against degradation by static electricity, the construction in which the address wires and data wires are short-circuited with a short-circuiting wire formed of a wiring material in a region outside the display region as disclosed in Japanese Unexamined Patent Publication No. 59,475/1986 has been known.
When the address wires and data wires are short-circuited in the manner described above, however, though the detection of a line defect in the address wires and data wires is attainable, the test for confirming the effective lighting condition of the component picture elements is not attainable unless the short-circuiting wire is cut off. Moreover, since the short-circuiting wire has been cut off by the time that the liquid crystal display device is completed, the produced construction is susceptible to the influence of static electricity.
To cope with this problem, the idea of establishing electrical interconnection severally between the address wires and data wires or between the individual wires as through the medium of a two-terminal operation thin-film transistor has been conceived as disclosed in Japanese Unexamined Patent Publication No. 220,289/1988, for example.
Since the short-circuiting wire for establishing electrical interconnection between the address wires and other wires as described above is formed as disposed in the region outside the display region, namely along the periphery of the liquid crystal-driving active matrix substrate, however, it has the problem of readily succumbing to wire disconnection due to breakage after the produced substrate is cut out in a prescribed size. Though this problem can be coped with by interposing a gap of at least several hundred .mu.m between the outer edge of the substrate and the short-circuiting wire, this insertion of the gap entails the problem of enlarging the substrate.
Besides, since the two-terminal operation thin film transistor which is interposed between the address wires and other wires and the short-circuiting wire is subjected to application of static electricity of fairly high voltage, it has the problem of readily succumbing to wire disconnection due to breakage caused by the static electricity.
There are times when the gate electrode of the two-terminal operation thin-film transistor is formed on the short-circuiting wire through the medium of an insulating film. Since the leading terminal of the gate electrode is liable to sustain local damage by static electricity owing to the application of the static electricity of high voltage, the disadvantage ensues that the address wires and data wires leading to the gate electrode are short-circuited to the short-circuiting wire and, as a result, the confirmation of the effective lighting condition of the component picture elements becomes no longer obtainable. Once this short-circuit is suffered to occur, the disadvantage arises that a defective display will appear when the liquid device is turned on without separation of the short-circuiting wire.
In the conventional liquid crystal display device, the idea of establishing electrical interconnection severally between the address wires and data wires through the medium of the two-terminal operation thin film transistor is conceived as described above for the purpose of protecting the device against the mischief of static electricity and detecting a point defect during the process of production. When the substrate is cut out in the prescribed size, the problem of the short-circuiting wire readily succumbing to disconnection due to breakage, the problem of the two-terminal operation thin-film transistor readily succumbing to disconnection due to breakage caused by static electricity, and the problem of the address wires and data wires being readily short-circuited to the short-circuiting wire due to local breakage of the leading terminals of the date electrode by static electricity are liable to occur.